The present invention, in some embodiments thereof, relates to multiple-input multiple-output (MIMO) communication systems and, more particularly, but not exclusively, to methods and apparatus for using sequences for symbol timing synchronization in single-carrier modulation MIMO communication systems.
The term “single-carrier modulation” in all its grammatical forms is used throughout the present specification and claims to mean a modulation of a single carrier frequency.
Some non-limiting examples of single-carrier modulation include Quadrature Amplitude Modulation (QAM) and Phase Shift Keying modulation.
Communication systems in which the transmitted signal is emitted from several separate transmitting devices at one end of a communication link and is processed using signals from several receiving devices on the other side of the link are termed multiple-input multiple-output (MIMO) systems.
As an example we may consider several antennas located on one side of a link, each of them transmits a different signal, all signals are transmitted simultaneously using the same carrier frequency.
On the other side of the link we have several receiving antennas, each of which receives a slightly different signal due to being in a different position and possibly having a different radiation pattern. The received signals are typically processed together.
It is known that MIMO systems have a potential to significantly increase the efficiency of the communication systems. Such systems are capable of distinguishing between several signals transmitted simultaneously.
In practice many deployed MIMO communication systems use an OFDM or generally a multi-carrier modulation. Multi-carrier modulations such as OFDM greatly simplify timing synchronization at the receiver side. In OFDM timing offsets do not affect the frequencies of the multiple carriers, and appear as a shift in phase, easily correctable.
A special case related to MIMO systems is transmission in two polarizations. This concept is used in point-to-point microwave backhaul systems. In dual-polarization systems two signals are transmitted simultaneously using orthogonal polarizations of the electromagnetic waves. These signals are transmitted using the same carrier frequency, and generally interfere with each other at the receiving side. However, the mutual interference between the polarized signals is typically low. As an example, the interfering signal may by 20 dB lower than the desired signal.
Additional background art includes:
An article titled “Impact of Frequency Selective Channels on a Line-of-Sight MIMO Microwave Radio Link”, by Ingason, Liu, Coldrey, Wolfgang and Hansryd, published in 71st IEEE Vehicular Technology Conference, Taipei 2010, pp. 1-5.
An article titled “Maximum MIMO Capacity in Line-of-Sight”, by Sarris and Nix, published in Fifth international conference on information, communications and signal processing, Bangkok 2005, pp. 123-1240.
An article titled “Receiver structures for MIMO-SC/FDE Systems”, by Reinhardt and Huemer, published in 63rd IEEE Vehicular Technology Conference, Melbourne 2006, pp. 1401-1405.
An article titled “Construction and Capacity Analysis of High-Rank Line-of-Sight MIMO Channels”, by Bohagen, Orten and Oien, published in IEEE Wireless Communications and Networking Conference 2005, pp. 423-437.
An article titled “Modeling and Analysis of a 40 GHz MIMO System for Fixed Wireless Access”, by Bohagen, Orten and Oien, published in 61st IEEE Vehicular Technology Conference, 2005, pp. 1691-1695.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.